What does a stop (shown as st0p) message indicate on an H, J, or L frame breaker?

It may indicate that the trip unit is set up for a neutral CT but none is connected. If this is the case, it will clear by pressing OK twice when the NCT is installed or a jumper is placed between T1 and T2. If NCT is not installed, pressing OK will momentarily clear the STOP error, but it will come right back.

It may indicate a BSCM failure.

It may indicate an error with the trip unit. It is possible the trip unit connection was interrupted while the breaker was in operation and this error can be easily reset by unlocking the trip unit screen and pressing the OK button to acknowledge the error.

If pressing the OK button does not clear the error, the trip unit is damaged and the trip unit or breaker will need to be replaced.